All primary batteries generate electricity by chemical action and in all primary batteries the chemical action and the production of electricity stops when one of the electrodes is exhausted. Where batteries are essential to the operation of electrical apparatus such as telephones, signals and the like they must be replaced or repaired before they cease to function. For this reason, it is important to know the extent to which the electrode is used up, and to know the time when new electrodes must be furnished or when the entire primary battery is to be replaced.
The present invention provides a rugged mechanical battery life indicator, responsive to the dimensions of one or both of the electrodes. If the battery is a carbon zinc combination, only the zinc electrode is sensed and its thickness indicated. The indicator means is positioned at the top of the container for convenience of the user.
One of the features of the invention is the ability to use the exhaustion indicator with battery containers that are opaque. The indicators can also be used with electrolytes that are not transparent.